Vegetation and soils of the Meikle Kilrannoch ultramafic sites

Summary

The vegetation of two ultramafic sites (MK1 and MK2) at Meikle Kilrannoch are described. MK1 is dome shaped and has much weathering bedrock whilst MK2 is flatter, lacks weathering bedrock and has probably been entirely peat covered. Six vegetation Groups were recognized: I, high-level blanket bog; II and III, grass heath (with II more sedge-rich); IV, dwarf shrub heath; V and VI, debris (an open vegetation on stony skeletal soils). Vegetation maps were produced which had five mapping units: Group I, Groups II and IH combined, Group IV, Groups V and VI combined, and non-vegetated eroding peat. Three main soil types occur: peat, which underlies Group I; a complex of freely draining magnesian brown soils and imperfectly drained magnesian gleys which bear Groups II–IV; and skeletal soils, derived either from weathering bedrock (MK1 only) or ultramafic drift, which bear vegetation in Groups V or VI. The rare plants are commonest in, but not restricted to, debris vegetation on skeletal soils. The likely plant toxicity of soil magnesium at the sites is reaffirmed but it is suggested that the low plant cover in the debris is more likely to result from low nutrients or intensive frost action or both. Floristic differences between MK1 and MK2 are discussed and quantified for Lychnis alpina (which had 68000individuals on the former site and 46 on the latter) but the causes of the differences remain unexplained.     

Vegetation composition of a maritime salt marsh in Qatar in relation to edaphic features

Abstract. Coverpercentage values for plant species were estimated using the line-intercept method along two belt transects starting at the lower mangrove frontier and ending at the upper height of the salt marsh. Twelve perennial species representing five growth forms were recorded with a total cover ranging between 10 and 50 %, depending on the type of substrate. Principal components analysis of the soil data indicated an array of stands, on the basis of which four vegetation zones couldbe distinguished. The procumbent growth form predominating on the salt marsh is related to high salinity levels. The procumbent vegetation shows a zonation related to the degree of waterlogging. The rhizomatous growth form is found on sites with a low bicarbonate content and saturation percentage levels, while the undershrub- and stoloniferous growth forms occupy sites of low salinity level, linked with intermediate values of the other edaphic factors.     

Distribution ofUrtica dioica L. in relation to edaphic factors

Summary Soils withU. dioica (a soils) were compared with soils 1–6 m away (b soils) with seemingly identical conditions except for absence of Urtica. The a soils had a higher EDTA–Cu concentration than b soils. The values for mineralised N, anion exchanged P, CEC, conductivity, Zn, Ca, Mg, K, organic matter and pH were alike in a- and b soils. Inorganic P was a limiting factor for Urtica when the P level, in general, was low (in this material not roadside soils). In the roadside soils the level of inorganic P was, in general, high and the content in a- and b soils was alike.     

Species diversity in plant communities on ultramafic soils in relation to pine afforestation

Abstract. The influence of pine afforestation on the species diversity of plant communities on ultramafic substrate was investigated in an area of Tuscany, central Italy, by means of species-area relationships, plant unit area, the Gini coefficient and the pattern of the index of Jaccard in relation to plot size. The species-area relationship was found to best fit the semilogarithmic model. Contrary to the available data for temperate ecosystems, tree canopy cover was found to increase the α-diversity of the understorey vegetation and its cover. The nutrient input due to the pine canopy caused an increase in the abundance of the grass Festuca inops — which was already present in the community — and subsequently the spread of several grassland species leading to a reduction in dominance concentration and to the formation of a species-rich grassland. The pine cover caused a decrease in floristic resemblance between plots, especially when the canopy cover is scattered. The increase in species richness found under the pine canopy, where the metal content in the soil is higher, suggests that potentially toxic metals are not the most limiting factor in Tuscan ultramafic soils. The typical poorness of vegetation on ultramafic soils should be first of all related to hydrological and nutritional stresses.     

崇明东滩盐沼植被成带性对土壤因子的响应

对东滩湿地不同植被带与土壤环境因子的关系进行了探讨,分析植被成带性分布与土壤含水量、土壤盐度、土壤温度之间的关系,研究表明:(1)光滩(TF)、海三棱藨草(Sm)、互花米草带(Sa)土壤含水量差异显著(P0.05),随着土壤含水量的显著变化,海三棱藨草和互花米草种群分布呈现明显带状分布,土壤含水量对植被带的分布起到一定的平衡作用,在土壤经常性淹水下,互花米草种群的海向性拓殖受到一定抑制。(2)光滩带、海三棱藨草带、互花米草带之间的土壤盐分(NaCl)差异极显著(P0.001),从海向陆依次为:NaCl光滩带NaCl海三棱带NaCl互花米草带,NaCl含量增加土壤含水量相对减小,土壤盐度和含水量的差异极大影响了海三棱藨草和互花米草植被带的分布模式,从而进一步制约了其演替进程。不同植被带间温度差异显著,总体趋势为互花米草带最高而潮滩带最低,并且互花米草带土壤温度显著高于其它各带,小尺度空间上植被对环境因子的响应明显。(3)相对于7月份而言,5月份各带内土壤含水量显著较高,但植被带间没有显著性变化。光滩最高,依次为海三棱带和互花米草带。然而,7月份土壤盐度和温度显著大于5月份,互花米草带最高,依次为海三棱和光滩带。     

Soil pH and electrical conductivity are key edaphic factors shaping bacterial communities of greenhouse soils in Korea

Soil microorganisms play an essential role in soil ecosystem processes such as organic matter decomposition, nutrient cycling, and plant nutrient availability. The land use for greenhouse cultivation has been increasing continuously, which involves an intensive input of agricultural materials to enhance productivity; however, relatively little is known about bacterial communities in greenhouse soils. To assess the effects of environmental factors on the soil bacterial diversity and community composition, a total of 187 greenhouse soil samples collected across Korea were subjected to bacterial 16S rRNA gene pyrosequencing analysis. A total of 11,865 operational taxonomic units at a 97% similarity cutoff level were detected from 847,560 sequences. Among nine soil factors evaluated; pH, electrical conductivity (EC), exchangeable cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺), available P₂O₅, organic matter, and NO₃-N, soil pH was most strongly correlated with bacterial richness (polynomial regression, pH: R² = 0.1683, P < 0.001) and diversity (pH: R² = 0.1765, P < 0.001). Community dissimilarities (Bray-Curtis distance) were positively correlated with Euclidean distance for pH and EC (Mantel test, pH: r = 0.2672, P < 0.001; EC: r = 0.1473, P < 0.001). Among dominant phyla (> 1%), the relative abundances of Proteobacteria, Gemmatimonadetes, Acidobacteria, Bacteroidetes, Chloroflexi, and Planctomycetes were also more strongly correlated with pH and EC values, compared with other soil cation contents, such as Ca²⁺, Mg²⁺, Na⁺, and K⁺. Our results suggest that, despite the heterogeneity of various environmental variables, the bacterial communities of the intensively cultivated greenhouse soils were particularly influenced by soil pH and EC. These findings therefore shed light on the soil microbial ecology of greenhouse cultivation, which should be helpful for devising effective management strategies to enhance soil microbial diversity and improving crop productivity.     

Species diversity in relation to ultramafic substrate and to altitude in southwestern New Zealand

Altitudinal trends in species diversity were examined on a New Zealand ultramafic mountain, and on nearby normal (schist) substrate. At lower altitudes, diversity is similar on the two substrates. On the ultramafic substrate, species diversity decreased with increasing altitude; on schist substrate the opposite trend was found. This difference was demonstrable in species richness, based on species presence/absence, and in indices of species diversity based on cover data (the ShannonH and the Simpson/Yule — InD). It is suggested that on ultramafics, altitudinal stress and soil conditions lead to a decrease in diversity with altitude. On schist, in contrast, the opening of the canopy with altitude is suggested to be the predominant influence, leading to an increase in diversity with altitude. Nomenclature: Allan, H. H. 1961. Flora of New Zealand, Vol I, Government Printer, Wellington; Mark, A. F. & Adams, N. M. 1986. New Zealand alpine plants. 2nd rev. Reed Methuen, Wellington; Connor, H. E. & Edgar, E. 1987. Name changes in the indigenous New Zealand Flora, 1960–1986 and Nomina Nova IV, 1983–1986, N.Z. Jl Bot. 25: 115–170; except where indicated.     

Distribution of some daily and seasonal events in relation to changes of physical factors

A special case of the Weibull distribution model is used in describing the course of behavioural transformation processes in relation to some cyclic physical factor. The model assumes that the rate of the process increases, the less inhibiting the physical factor, and the faster the factor changes. However, due to some resistance or a depletion, the rate slows down, the further the process progresses. The model was tested on the daily onset of activity in nocturnal insects, daily roosting flight of blackbirds, dark and light adaptation by pigment migration in insect eyes, photoperiodic response of an insect, and daily emergence of tiger beetles. The assumptions of the model are tested and discussed. One of these is violated in unnaturally fast changes of the physical factor because the process reaches some constant minimum duration, and proportionality between rate of process and rate of factor can no longer be maintained.     

Distribution ofUrtica dioica L. andRubus fruticosus L. (+agg.) in relation to edaphic factors in cultivated poplar woods

Urtica dioica L. andRubus fruticosus L. (+agg.) are widely distributed in Belgian cultivated poplar woods. Using adjusted standardized residuals as an objective measure of preference of a species for ecoparameters, it seems possible to describe the distribution betweenUrtica andRubus as coincidental as regards ecological considerations. Both plant species behave obviously as antagonists.     

Assessing mineralization rates of petroleum hydrocarbons in soils in relation to environmental factors and experimental scale

Mineralization rates of non-volatile petroleum hydrocarbons (HCs) in five different oil-contaminated soils with initial HC contents ranging from 0.1 to 13 g kg^-1 are estimated as a function of environmental factors. The aim of the study is threefold, (i) to study the relevance of environmental factors that may influence the mineralization rate, (ii) to compare mineralization rates estimated in two experiments at different scales, after standardizing them to environmental reference conditions, (iii) to evaluate the CO₂ production rate as a measure for the mineralization rate of HCs. Experiments were performed at laboratory scale (30–50 cm³ soil volume) in closed-jars under constant environmental conditions and in lysimeters (0.81 m³ soil volume) under dynamic climatic and hydrological conditions. A biodegradation model, coupled to transport models for soil heat, water, and gas dynamics is employed for data interpretation. The transport models are used to simulate the environmental conditions that influence the mineralization rate in the non-steady lysimeter experiments. The results show that temperature, O₂ concentration and HC content have an effect on the mineralization rates. Water content could not be identified as a direct governing environmental factor. However, an indirect effect of water content is that it influences the effective gas diffusion coefficient in soils. The CO₂ production rate seems to be a good quantity to express the mineralization rate of HCs for HC contents>1 g kg^-1. Measured CO₂ production rates standardized to reference conditions are similar for the two different experimental scales. This demonstrates that the usage of biodegradation rates obtained in the laboratory to predict the biodegradation rates under field conditions is sound, as long as the differences in environmental conditions have been taken into account.     

Adaptation of sweet corn to English climatic,edaphic and biotic factors

Summary A review is given of diseases and pests attacking North American inbred, hybrid and open-pollinated strains of sweet corn in England. Genetical and environmental influences are considered as problems of adaptation. Cold tolerance, susceptibility to smut, and fungi attacking ripening grain are under genetical control, but modified by environmental conditions. Analysis of these factors helps to control these diseases. Strains differ in resistance to frit fly attacks, and this is modified by sowing time. Frit flies and wireworms, acting independently or together, may limit sweet corn growing in some areas, while aphids also attack some inbred lines. Various methods of insect control are suggested. Mice and birds eat seeds, and bird damage may also limit maize growing. An outline suggests genetical and non-genetical modes of future control for diseases and insect pests when adaptating sweet corn to new climatic and other factors. These include selection for and use of resistant strains, or control by sowing at specific times.     

Phenological modifications in plants by various edaphic factors

Various mechanical, chemical and physical soil analyses were carried out, in addition to weather observations, for 3 years at several sites along an oceanic-continental gradient in a fjord district in western Norway. All the environmental factors observed were correlated with the spring and a few late-season phenophases of many native and cultivated woody plants and some herbs by simple, linear correlations and by stepwise multiple and partial analyses. Different techniques were used to try and eliminate many intercorrelations between various environmental factors. As expected, air temperature measurements in nearly all analyses from these temperate region districts gave the most significant correlations with the phenology of the plants, the temperature during the night generally being the most important in mainly vegetative periods, e.g. to leaf bud break in spring, and the temperature during the day affecting the more generative phases, such as the period between leaf bud break and flowering. The other environmental factors, however, showed strong variation in correlation significance among the various species studied and also with different phenophases of the same species. Various hypotheses are put forward to explain such variation. Air humidity (including precipitation) and /or soil moisture (including intercorrelated parameters, e.g. soil grain size and bulk density) were relatively often found to be of importance. In the stepwise multiple analyses for leaf bud break of the birch (Betula pubescens), for instance, the amount of precipitation was the second factor to enter the analyses by a positive correlation with the developmental rate, after the most important factor, the night temperature. Positive correlations with a high clay content and bulk density in the soil indicated that high soil moisture is also favourable for early bud break in the birch. Other phenophases that seemed to be favoured by a good water supply were leaf bud break of the bird cherry (Prunus padus) and rowan (Sorbus aucuparia), and flowering of the hazel (Corylus avellana), common lilac (Syringa vulgaris), plum (’Victoria’) and currant (’Red Dutch’) and also, to some degree, the goat willow (Salix caprea). The amount of ions (P, K, Mg and Ca) often showed negative correlations with the developmental rate, particularly of earlier phenophases of both native and cultivated plants (except for the apple ’Gravenstein’ and pear ’Moltke’), possibly, indicating that a high nutrient level delayed plant development. A similar explanation might be given for the observation that high pH in the soil often seemed to delay plant development (leaf bud break of Betula, Sorbus, Syringa and plum, and flowering of Corylus, bluebell (Campanula rotundifolia) and red currant). According to the analyses there seemed to be a tendency for plants that are particularly dependent on warm weather for leaf bud break, e.g. the ash (Fraxinus excelsior), and flowering, e.g. Prunus, pear, apple and, to some degree, the raspberry (’Preussen’), to be less dependent on other environmental factors for their development. For instance, if there were any effects of water for these plants, they were negative for moisture and soil factors intercorrelated with water. Received: 25 October 2000 / Revised: 9 May 2001 / Accepted: 24 May 2001     

Vegetation gradients in relation to temporal fluctuation of environmental factors in Bekanbeushi peatland, Hokkaido, Japan

The relationship between vegetation gradients and temporal variation of groundwater table depth, groundwater pH and electrical conductivity was studied in Bekanbeushi peatland, northern Japan. These environmental factors were expressed using four statistical parameters: maximum, minimum, mean and standard deviation or coefficient of variation during the growing season. The bog–fen–swamp/marsh gradient was primarily explained by minimum, maximum and mean groundwater table depth and minimum pH. The separation between the bog and the fen by minimum pH was particularly clear. Minimum conductivity was secondarily important for explaining this vegetation gradient. The swamp–marsh gradient was explained by the standard deviation of groundwater table depth. Maximum pH and conductivity were not significant in explaining either of these gradients. This study suggests that parameters that are obtained from the consecutive measurement of environmental factors may have differing significance in explaining vegetation gradients in these peatlands, and values from a single sampling may miss important ecological information.     

Ecotypic response to ultramafic soils by some plant species of northwestern United States

Soils high in magnesium derived from ultramafic rocks (serpentine, peridotite, and dunite) in northwestern United States support endemic as well as wide-ranging but edaphically indifferent(bodenvag) species. The latter occur widely on diverse rock formations of the region. Severalbodenvag species are shown to respond ecotypically to ultramafic soils. Of 18 species tested, all but three are differentiated into strains either tolerant or intolerant of ultramafic soils. Tests for edaphic preferences were conducted with seedlings and mature transplants on ultramafic soils. Growth performances were determined in greenhouse pot tests, outdoor soil bins, and by transplants in the wild. Herbaceous perennials (e.g.,Achillea millefolium, Fragaria virginiana, Prunella vulgaris, Rumex acetosella) gave the clearest ecotypic differences. Woody species either showed only slight ecotypic response(Spiraea douglasii var.menziesii andGaultheria shallon) or delayed the expression of their genotypic adaptability(Pinus contorta). Where ultramafic abut non-ultramafic soils, those populations ofbodenvag species that grow in non-ultramafic habitats can have a significant proportion of individuals tolerant to ferromagnesian soils (e.g.,Achillea millefolium). This suggests gene flow between populations of contrasting edaphic sites and possibly preadaptedness for the ultramafic habitat. Strains of two introduced weeds(Prunella vulgaris andRumex acetosella) have become ecotypically tolerant to ultramafic soils, probably within the last 75 years.     

Analysis of spatial and semporal organization in a salmonid brook in relation to physical factors and macrophytic vegetation

Four compartments of a salmonid brook were studied in consecutive sections either at sector scale or at facies scale: physical features, water quality, macrophytes and salmonids. The most important factor in the spatial and temporal organisation was the longitudinal zonation assessed by the four compartments. It was mainly shown by a gradient of the length of the morphodynamic sequence and of the facies width, of the pH and the conductivity and of macrophyte cover. It induced a colonisation by older trout in the downstream part of the brook where growth was better and shelter given by the bankside vegetation was more abundant. There were also greater densities of other age-classes upstream, with a correlation between salmon and rock shelter. Furthermore, the second factor corresponded to the flow characteristics and a granulometry gradient. The third factor corresponded chiefly to lighting, salmon numbers and densities. Salmonids showed a temporal stability from spring to autumn,and an opposition between growth and density. Six clusters of sectors defined functional entities. With regard to the 3—dimensitnal structure of the brook, the special pattern of each compartment shows its contribution to the functioning of the whole. Taking into account the scale of the study, the coexistence between trout and salmon did not show a competition between the two species, but rather a spatial partition, thanks to thehheterogenity inside each sector. We concluded on the necessity of studying sympatry at the facies scale to assess the role of habitat factors as regulators of carrying capacity.     

Species richness vs evenness: independent relationship and different responses to edaphic factors

The main components of species diversity are richness and evenness. Species richness has been the subject of biodiversity studies more often than species evenness. Some simulated models suggest that the relationship between these two components is equal and predictable in a stable environment. This study was conducted in a human-shaped and unstable environment in arable field boundaries. A total of 30 sampling plots were laid out at random in the boundaries. Vegetation at the sites was of meadow type. The relationship between species richness and evenness, and their responses to edaphic nutrient factors in the field boundaries, were examined by correlation analysis and an ordination method. Correlation analyses demonstrated that no consistent pattern was present in the relationship between species evenness and species richness in this human-shaped ecosystem. Species richness and evenness also had different responses to edaphic factors, with species richness being negatively correlated with phosphorus, and species evenness negatively correlated with the ratio of organic carbon to total nitrogen in soil. The results indicate that different and independent ecological processes determine species richness and evenness. The relationship between these two components may be site-specific, reflecting variation in resource utilization by plant species. The pattern thus reflects the spatial heterogeneity of disturbances or 'patchiness' of resources between sites in a semi-natural ecosystem.